The present invention relates to video recorder and playback systems, and more particularly to controlling the presentation of content.
Television (TV) content distribution is quickly migrating from analog formats to compressed digital formats. Currently, distribution of digital video content for TV display is dominated by use of the MPEG-2 video compression standard (ISO/IEC 13818-2). MPEG-2 and its predecessor MPEG-1 define the standards to compress video content using a combination of various techniques. An MPEG-encoded stream may have three types of pictures, Intra-coded (I), Predicted (P) and Bi-directionally predicted (B). I-pictures are not compressed using any temporal predictions and can be decoded without the need of any other picture. The P-pictures perform temporal predictions from a picture that comes before it in the display order. Thus, decode of a P-pictures requires one picture (from the past) to be available with the decoder for performing temporal predictions. This prediction picture may be either an I-picture or another P-picture. The B-pictures are bi-directionally predicted and, hence, use two pictures for prediction, one from the past and another from the future (in display order).
During normal decode of MPEG streams, video decoders store the last two decompressed I/P pictures in memory. The last I/P picture is used for predicting an incoming P-picture and the last two I/P pictures are used for predicting an incoming B-picture. During a Rewind operation, the pictures have to be displayed in the reverse order. The video stream is itself fed to the decoder through a system that first recorded the stream on a recordable media such as a hard-disk. A Rewind operation is complex because B-pictures cannot be decoded from the previously decoded pictures in the rewind order. Rather, the last two prediction pictures in the forward decode order are needed by the decoder in order to decode a B-picture.
The foregoing can be accomplished by decoding pictures in the forward picture order starting from the last I-picture before the B-picture in the forward decoding order. Thus, an existing decoder has to decode multiple pictures for displaying a single picture. If such a decoder is unable to decode multiple pictures in the given time limit for getting ready with a new picture for display, then the video quality suffers.
Further limitations and disadvantages of conventional and traditional systems will become apparent to one of skill in the art through comparison of such systems with the invention as set forth in the remainder of the present application with reference to the drawings.